Such devices exist and are necessary at the end of a track in maintenance workshops and repair workshops, sidings, etc., for vehicles running on guide rails such as railway lines, for example.
These devices are not designed to stop vehicles running at high speed, but are provided for safety purposes to bring finally to a standstill vehicles which should normally stop before striking the device but which may, however, strike it at low speed, for example at the most a few km/h, due to the inaccuracy of the operator's driving.
Despite the low speed at which the vehicle is liable to strike the device, the kinetic energy of the moving unit is, however, very great because of the mass of the train. The device must therefore be strong and the scotch block must be high enough to prevent the vehicle wheel from passing over it. The normal necessary height is about fifteen centimeters.
However, it can happen that the base of the vehicle body is not as high as the required height above the rail, and is, say, six centimeters. That is a 6-centimeter scotch block is not high enough.